Sea anemones and jellyfish

To be finalised during Consultation.

What we need to do and where
Glaucous pimplet - Keith Hiscock

Glaucous pimplet, Keith Hiscock

St. John's jellyfish, Eleanor Goodall

St. John’s jellyfish, Eleanor Goodall

Snakelocks anemone

Snakelocks anemone

1. About

Devon’s coasts are teeming with life, much of it hidden beneath the waves or found along rocky shores and estuaries. Habitats from exposed headlands to sheltered coves support a rich tapestry of marine biodiversity, particularly in the intertidal zone. 

Devon’s intertidal rock pools are vibrant microecosystems brimming with life. They’re home to a diverse mix of invertebrates, including colonial bryozoans, sea squirts, encrusting and branching sponges, brittle stars, sea urchins, chitons, sea slugs, bivalves and more. 

Among the most visually striking invertebrates found here are the sea anemones and stalked jellyfish. These soft-bodied species belong to the cnidarian group. All cnidarians have stinging cells, also known as cnidocytes, which they use to capture prey and defend their territories. Despite their delicate appearance, they’re remarkably resilient to the dynamic and often harsh conditions of the shoreline. 

Significant habitats for these species include: 

Rocky shores 

Rocky shores provide ideal habitats for many sea anemones. They anchor themselves in crevices, beneath overhangs and in shaded rock pools to avoid drying out during low tide. 

Tidal pools 

Tidal pools retain water at low tide and so provide a stable microhabitat for more delicate cnidarians such as stalked jellyfish and smaller anemones. Unlike their free-swimming relatives, stalked jellyfish have a stalk they use to attach themselves to seaweed or rocks. They gently pulse to catch tiny prey. 

Seagrass and seaweed beds 

In more sheltered estuarine areas, dense growths of seagrass and seaweed provide excellent attachment points for stalked jellyfish. These habitats offer camouflage and a consistent supply of food. 

In Devon, places such as Wembury and Northam Burrows, are hot spots for these species. Their rocky outcrops, tidal pools and sheltered estuarine zones provide ideal conditions for both sea anemones and stalked jellyfish. 

Devon Species of Conservation Concern

Eight species of cnidaria are listed as Devon Species of Conservation Concern: 

  • Glaucous pimplet (Anthopleura thallia) 
  • Sea fir (Hartlaubella gelatinosa) 
  • Trumpet anemone (Aiptasia couchii) 
  • Scarlet and gold star coral (Balanophyllia regia) 
  • Kaleidoscope jellyfish (Haliclystus auricula) 
  • Spotted kaleidoscope jellyfish (Haliclystus octoradiatus) 
  • St John’s jellyfish (Calvadosia cruxmelitensis) 
  • A Stalked jellyfish (Calvadosia campanulata) 

Key pressures and opportunities

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Coastal development

Building sea defences, harbours and housing near the coast can reduce habitat, especially in intertidal zones. It disrupts the natural structures, reducing the availability of crevices, pools and sediment types these species rely on. 

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Pollution

Runoff from agriculture, sewage discharge and marine litter (especially plastics and microplastics) can degrade water quality. Cnidarians are particularly sensitive to chemical pollutants, which can make them less able to reproduce or, at worst, kill them. 

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Climate change

Rising sea temperatures and ocean acidification can change the distribution of species and disrupt their reproductive cycles. For example, cnidarians may experience stress or bleaching. 

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Recreational disturbance

Rockpooling, trampling and boating can physically damage fragile habitats. Even well-meaning visitors can unintentionally dislodge sea anemones from their footing. 

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Invasive species

Non-native species, such as xxx, introduced through ballast water or aquaculture can outcompete or prey on native cnidarians, changing the balance of intertidal ecosystems. 

2. What we need to do and where

Priority

Increase the abundance and distribution of sea anemones and stalked jellyfish, particularly those identified as Focus Species.  

Focus species

Glaucous pimplet - Keith Hiscock

Glaucous pimplet

Anthopleura thallia
Read more

To be finalised during Consultation. 

The glaucous pimplet is a small but distinctive species of sea anemone found on wave-exposed rocky shores on the north coast of Devon, such as Lee Bay, Croyde and Westward Ho! Devon hosts one of the highest populations of this species in the UK, so is a key region for its conservation and study. 

The glaucous pimplet is typically found in shallow rock pools, crevices and areas among dense mussel beds, often partially buried under gravel or sediment. Its trumpet-shaped body is dotted with sticky bumps, also known as verrucae, that trap sand and bits of debris, helping it blend into its surroundings. 

It can be green, brown or greyish with up to 100 retractable tentacles that are a similar colour or subtly patterned. Its tentacles are arranged in whorls around its mouth and have small outgrowths called acrorhagi that are armed with stinging cells for defence. Though not widely distributed, it can be locally abundant and is thought to reproduce asexually, forming groups of genetically identical individuals. 

The glaucous pimplet is small and is often buried or camouflaged, making it vulnerable to trampling or to being accidentally removed. It often lives among mussels, so any decline in mussel populations (due to harvesting or environmental stress) could reduce their habitat. Consultation Q: What are the key pressures? 

Stalked jellyfish

Read more

To be finalised during Consultation. 

Stalked jellyfish are a rare and unusual type of jellyfish that live in shallow coastal waters. Instead of floating freely in the water, they have a stalk they use to attach themselves to seaweed, seagrass or rocks. They can be hard to spot as they’re small, growing to about 5 cm wide, and blend in with their surroundings.

There are ten species recorded in the UK, with four commonly found in Devon. Each has a central body with eight arms and clusters of tentacles at the end of each arm. In some species the tentacles are filled with stinging cells that help catch tiny prey such as plankton. 

Spotted kaleidoscope jellyfish

Haliclystus octoradiatus

To be finalised during Consultation. 

The spotted kaleidoscope jellyfish is a small, stalked jellyfish found in the shallow, sheltered waters of Devon’s intertidal zones. Like stalked jellyfish (above), it has a small stalk that it uses to anchor itself to seaweed, seagrass or small stones. Its body is bell-shaped and vividly patterned, often with a mosaic of translucent greens, browns or oranges and distinctive white spots, the features that give it its common name. 

This species is typically found in rock pools, estuarine lagoons, and seagrass beds, where it uses its tentacles to capture tiny invertebrates. Though small and easily overlooked, it plays a role in the local food web and is an indicator of healthy, undisturbed intertidal habitats. Its presence suggests good water quality and intact microhabitats, making it a valuable species for monitoring environmental change. 

Kaleidoscope jellyfish

Haliclystus auricula

To be finalised during Consultation. 

St. John's jellyfish, Eleanor Goodall

St John’s jellyfish

Calvadosia cruxmelitensis

To be finalised during Consultation. 

Calvadosia campanulata - Keith Hiscock

A stalked jellyfish

Calvadosia campanulata

To be finalised during Consultation. 

Actions for all sea anemones and stalked jellyfish

Habitat management and creation

Intertidal invertebrates are found across Devon’s coastlines and will benefit from the actions set out on the Coast page. Anyone who is managing or creating habitat for sea anemones and stalked jellyfish should be aware of their needs. See the list of Devon Species of Conservation Concern and Find out more below for more information.

Protect sensitive intertidal invertebrate habitats 

  • Identify and map areas where sensitive intertidal invertebrates, such as the glaucous pimplet, are known to occur, particularly wave-exposed rocky shores with gravelly rock pools. 
  • Include these habitats in local marine conservation designations and shoreline management plans. 
  • Use signage, codes of conduct and public education to promote responsible rockpooling and coastal recreation in areas with vulnerable species. 
  • Collaborate with local tourism operators to reduce trampling and disturbance in sensitive intertidal zones. 

Research and monitoring 

  • Fund research into reef resilience, the impact of climate change and potential restoration techniques. 
  • Explore pilot projects to restore reefs in degraded areas using natural or artificial substrates. 

3. Inspiration

Case studies

There’s lots of great work going on across Devon for sea anemones and stalked jellyfish. For example:

Wembury Marine Centre (Devon Wildlife Trust)

Wembury Marine Centre runs guided rock pool safaris and educational activities that help people identify and understand the importance of intertidal species like sea anemones and stalked jellyfish. The centre builds community support for marine conservation and encourages responsible shoreline behaviour. 

Where to visit

Always follow the Countryside Code and keep to footpaths and sites that are managed for public access.  

Wembury 

This rocky shoreline along Devon’s stunning south coast is one of the best places in the UK to discover the hidden wonders of marine life. At low tide the rock pools come alive with colourful sea anemones, darting shrimp, feathery worms and even the occasional starfish or sea urchin. 

Lee Bay 

Lee Bay’s peaceful setting and rich biodiversity make it an ideal spot for rockpooling, nature walks and discovering the fascinating invertebrates that live here.

For information on these and other sites that are open to the public please see the Explore Devon website.    

4. Find out more

Ask for useful links during the Consultation  

Marine Invertebrates – Field Studies Council 

Beneath the waves | Devon Wildlife Trust 

Home | Wembury Marine Centre 

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